This invention relates to the field of indicator light assemblies and more particularly to such assemblies that include lenses that contain fluorescent dyes.
To indicate equipment status, visual feedback is often provided in the form of a light source or "indicator light" which is activated when a predetermined equipment condition occurs. A lens is typically placed in front of the indicator light to soften the intensity of the light, change its color, or to disperse, focus or redirect the light.
In the design of electronic equipment, the general trend has been to reduce the overall size of the equipment. This is particularly true in the selective call radio paging receiver market where recently designed "pagers" are now available that can be carried in a shirt pocket. Such designs typically include a rectangular parallelepiped plastic housing that contains a single printed circuit board with appropriately attached electronic components. The housing is typically not much wider than the thickness of the printed circuit board and components. Therefore, if an indicator light assembly is to be installed in such a pager, a low profile assembly is required.
Although older paging receiver designs convey the received message to the user immediately upon receipt, recently developed paging receiver designs store a received message in the pager for later retrieval by the user. Therefore, it becomes necessary to inform the user that a message has been received. This is typically accomplished by sounding an alert tone, flashing a light, activating a vibrator, or, in the case of a digital display pager, causing a predetermined symbol to appear in the paging receiver's display. If a visual indication is desired, the current drain of the light source becomes critical because paging receivers typically have a very limited battery capacity. Therefore, to reduce battery drain while maintaining the output light intensity at an acceptable level, it would be desirable if the light from the light source could be collimated and directed in the general direction of the user's eyes.
In the previously described typical paging receiver design where a printed circuit board is enclosed in a plastic parallelepiped housing, the pager is usually worn such that the printed circuit board is parallel to the body; for example, when the pager is worn on a belt or carried in a shirt pocket, the printed circuit board is usually positioned parallel to the body. Therefore, if a light source were attached to the printed circuit board, the general direction of the light emitted from the source would be perpendicular to the board and, consequently, away from the user's eyes. Therefore, it would be desirable if a lens could be placed in front of the light source that would redirect the light in the general direction of the user's eyes, i.e., parallel to the printed circuit board.
In summary, there is a need for a low profile indicator light assembly that utilizes a low power light source attached to a printed circuit board. This low profile indicator light assembly should collimate the light emitted from the light source and redirect it in a direction parallel to the printed circuit board. In addition, it would be desirable if the light emitted from the assembly were of one color.
A prior art indicator light assembly is illustrated in FIG. 1. This assembly is used in plug-in modules manufactured by the Tektronixs Corporation for their 7000 series oscilloscopes. Referring to FIG. 1, a light source 100 emits light in a variety of directions. Of particular significance is the light emitted in the vertical direction; for example, light ray 102. Translucent plastic push buttons 104, 106 and 108 partially project out the front (to the left) of a chassis 110. In the figure, push button 106 is shown in its depressed position. An appropriate mechanism (not illustrated) latches the depressed push button in its depressed (right most) position while releasing the previously depressed push button to return to its undepressed (left most) position. Thus, only one push button can be held depressed at any one time. An appropriate multi-pole electrical switch assembly (not illustrated) is connected to the various push buttons to selectively activate corresponding circuits in the module. The construction of the mechanical mechanism and the multi-pole switch are unimportant for the purposes of this discussion and only the optical properties of the assembly will be discussed in detail.
When one of the push buttons is depressed, for example push button 106, light ray 102 strikes the bottom surface 106a of the push button at a 90 degree angle and is transmitted through the surface and upwards through the plastic without any change in its direction. Diagonal surface 106b of push button 106 is positioned at an angle of 45 degrees relative to bottom surface 106a. According to the principles of total internal reflection, when light ray 102 encounters diagonal surface 106b, it is reflected 90 degrees to the left. Light ray 102 then travels the length of push button 106 whereupon it strikes front surface 106c at a 90 degree angle and is transmitted through the surface, whereupon it becomes visible to the user.
If a different push button is depressed, for example push button 104, switch button 106 is released and moves to the left to its undepressed position. Switch button 104 then moves to the right whereupon it will intercept light ray 102 which will be reflected by diagonal surface 104b and transmitted through front surface 104c.